I think the whole spirit of the cart is to build to your own spec/artistic flair/ability/finances/time constraints,obviously if any of these are an issue or a "for sale" cart has something in particular you need then buying someone elses(insert from above)cart becomes a reality.As the sport progresses competitors will want to progress with it and new carts will be the route many will take and the old cart now redundant and taking up space could easily get someone else into the sport.

Clearly you're right that the vast majority of racers want to build their own, and that as the sport grows then there will be an increasing number of second hand carties from teams who build new racers or move on to other things. To a certain extent, that is happening already. However, there does seem to be a quite large gap between what people think their old cartie is worth and what people are actually prepared to pay for it. Basically, it seems that people who want to buy into the sport don't want to pay enough even to cover the cost of the component parts.

Pretty much like every other sport(especially motorsport) Component costs are horrendous and are rarely appreciated by a potential "2nd buyer",these are also the people who have never bought a length of steel a 2nd hand welder and spent hours hacksawing and grinding trolling ebay for parts and generally putting a lot into a hobby for very little return.Really if someone is serious about the sport they will have to learn it comes with a price wether that is paying for someone elses time or paying for it with their own that as they say is the end of that!